Conventionally, an I-shape wire used for producing oil rings mounted on pistons of internal combustion engines has been provided with oil holes I-shape by stamping. In order to conduct piercing by stamping, it is necessary to prepare dies corresponding to individual product specifications.
In contrast, as disclosed in Patent Document 1 (see below), laser beam processing has been proposed as means for formation of oil holes in an I-shape oil wire. In order to form oil holes, the technique shown in Patent Document 1 does not need preparing dies corresponding to individual product specifications, and is advantageous in enabling formation of optional hole shapes and hole pitches by means of laser beam processing.
The method of producing steel oil rings shown in Patent Document 1 is advantageous in reduction of man-hour for piercing but involves a problem that solidified residues (herein below referred to as dross) generated by laser beam processing adhere to a surface of profile wires. When the dross remains, there is a risk that during operation of engines, the dross exfoliated from the oil rings is mixed in engine lubricant oil as a metal lump thereby damaging a cylinder wall.
In order to improve the influence of dross adhesion, Patent Document 2 discloses to use a high thermal energy density processing method (including the YAG laser method) together with an assist gas of oxygen or air, as heating means. Also, the document teaches to reheat the dross and blow out it at a backside of the wire. Patent Document 2 further teaches an effectiveness of a method of removing dross in inline by means of scrubbing (i.e. grinding, cutting or chipping) as measures against the dross problem.
Patent Document 1: JP-A-3-260473
Patent Document 2: JP-A-9-159025